That would be due to cost, ss headers are an unbelievable ripoff, something like 2.5 or 3k

I don't think a race team is concerned with costs like the average Joe. They run through tires and brakes that cost more. Super sprint is only around $1300 or so now. Also they mentioned design as a reason stating that considerable gains weren't worth it over cutting stock pipes. Plus I have seen 15 whp dynos too.